Add a composite node type.
Use a helper for defining property delegates.
Initial implementing of a Container which maps nested nodes to a flattened view.
Add a test for the Container.
Introduced Document.Container which provides a flattened view for nested nodes.
Add method to access original view to Container API.
Make Document.Controller compatible with new Container API.
Fix regression.
Quasi-Obsolete: fix Transformer.

However, the Transformer will die soon.
Fix regression.
First iteration on rewriting the Document manipulation.
Enable Container tests.
Next iteration on re-writing the DocumentController.
Some fixes and cleanup.
Update selections on undo/redo explicitely.

Before it was updated on general graph changes which was too noisy.
Use new graph API for the annotation index.
Make Container a first class citizen in Document's world.
Remove obsolete transformer.
Fix regressions.
Fix regression.